Optical Activity of Chiral Palladium Complexes [Si-O-PdMe(S-/R-BINAP)] Covalently Bound to Silica Through Grafting

The transfer of molecular chirality to solid surfaces is a focus of research due to its importance for practical applications. While several chiral metal complexes have been anchored to metal oxide surfaces via linkers, the optical properties of those with a direct covalent bond between the metal center and the support’s surface oxygen remained unexplored. This study reports the separate synthesis of both enantiomers of palladium(II)-methyl-BINAP complexes (2,2′–Bis(diphenylphosphino)–1,1′–binaphthylmethylpalladium(II)) on silicon dioxide. The precursors [PdMe2(S-BINAP)] and [PdMe2(R-BINAP)] were synthesized, characterized, and grafted onto partially dehydroxylated SiO2 to form PdMe(S-BINAP)/SiO2 and PdMe(R-BINAP)/SiO2. Solid-state NMR, infrared spectroscopy, and circular dichroism spectroscopy are consistent with site isolation and the structures of both enantiomerically pure surface complexes. The grafted complexes exhibit mirror-image CD spectra with features distinct from their molecular precursors, indicating that immobilization modifies their chiroptical response. The thermal stability of the surface complexes was studied by temperature-programmed experiments.